Sound absorption material and method of manufacturing sound absorption material

ABSTRACT

Described embodiments relate to a method of manufacturing a sound absorption material. The method comprises: forming a low density fibrous web to act as a porous bulk absorber, the fibrous web containing a proportion of bi-component fibres, each bi-component fibre having a core material and a sheath material around the core material, the sheath material having a lower melting point than the core material; applying a thin facing layer to the low density fibrous web, wherein the facing layer is adhesively compatible with the sheath material; heating the fibrous web to a temperature sufficient to soften the sheath material of at least some of the bi-component fibres; and pressing the facing layer and fibrous web together under low pressure such that at least part of the facing layer contacts the softened sheath material of at least some of the bi-component fibres to form an adhesive bond between the facing layer and the fibrous web.

TECHNICAL FIELD

The described embodiments relate generally to processes for manufactureof sound absorption material and materials produced by such processes.

BACKGROUND

Sound absorption materials are used in a variety of applicationsincluding motor vehicles, machinery and buildings. These materials actto reduce noise transmission and/or reflection in the particularapplication and can be made from fibrous materials.

It is desired to address or ameliorate one or more disadvantages orshortcomings associated with existing sound absorption materials and/ormethods of manufacturing such materials, or to at least provide a usefulalternative thereto.

SUMMARY

Certain embodiments relate to a method of manufacturing a soundabsorption material. The method comprises forming a low density fibrousweb to act as a porous bulk absorber, the fibrous web containing aplurality of bi-component fibres, each bi-component fibre having a corematerial and a sheath material around the core material, the sheathmaterial having a lower melting point than the core material. The methodfurther comprises applying a facing layer to the fibrous web, the facinglayer being adhesively compatible with the sheath material. The methodfurther comprises heating the fibrous web to a temperature sufficient tosoften the sheath material of at least some of the bi-component fibres.The method further comprises pressing the facing layer and fibrous webtogether under low pressure such that at least part of the facing layercontacts the softened sheath material of at least some of thebi-component fibres to form an adhesive bond between the facing layerand the fibrous web.

The facing layer may comprise a film layer having a thickness of between5 and 100 microns. The thickness may alternatively be between about 10and 25 microns. Alternatively, the thickness of the film layer may beabout 15 microns. The thinner the film, the better, as long as it hassufficient structural integrity to resist being damaged or destroyedduring normal handling.

The fibrous web may have a thickness of between about 4 and 50millimetres before being pressed together with the film layer.Alternatively, the thickness of the fibrous web may be between about 4and 25 millimetres. Although various thicknesses can be used for thefibrous web, a practical maximum thickness is about 50 millimetres and apractical minimum thickness is about 4 millimetres.

The low pressure under which the facing layer and fibrous web arepressed together may be such that the fibrous web is compressed bybetween about 5% and 80% of its thickness. This pressure may be appliedevenly across the fibrous web to increase bulk density substantiallythroughout the fibrous web.

The temperature to which the fibrous web is heated to soften the sheathmaterial of the bi-component fibres depends upon the physical propertiesof the sheath material. For a polyethylene sheath, the temperature maybe about 140° C. to about 160° C. Alternatively, the temperature may beabout 150° C. For a polypropylene sheath, the temperature may be higher,for example about 180° C.

According to some embodiments, the method may further comprise applyinga second facing layer to a second face of the fibrous web, the secondfacing layer being adhesively compatible with the sheath material. Thepressing may comprise pressing the second facing layer and the fibrousweb together under low pressure such that at least part of the secondfacing layer contacts the softened sheath of at least some of thebi-component fibres to form an adhesive bond between the second facinglayer and the fibrous web. The second facing layer may comprise the samematerial as the first facing layer. Alternatively, the materials of thefirst and second facing layers may be different, in which case thethicknesses of the facing layers may be different.

According to further embodiments, the fibrous web may be a first fibrousweb and the method may further comprise pressing a second low densityfibrous web together with the second facing layer under low pressure toadhere a first side of the second fibrous web to the second facinglayer. The second fibrous web may comprise a proportion of bi-componentfibres that each have a core material and a sheath material in themanner of the bi-component fibres described above in relation to thefirst fibrous web.

The method may further comprise, prior to pressing a second fibrous webtogether with the second facing layer, applying an adhesive substance tothe first side of the second fibrous web. The adhesive substance may beadhesively compatible with both the second facing layer and the secondfibrous web. The adhesive substance may be provided in the form of a hotmelt adhesive powder, web, net, spray, or film form. The method mayfurther comprise activating the hot melt adhesive substance just priorto bringing the second fibrous web into contact with the second film, soas to form a permanent bond between the two layers. The hot meltadhesive may comprise one of a polyethylene, polypropylene, EVA, orpolyamide, or other adhesively compatible polymer with an appropriatemelt temperature. The adhesive substance may also comprise a water orsolvent based adhesive system, or may comprise a pressure sensitiveadhesive applied in accordance with known lamination processes.

The method may further comprise applying a third facing layer to asecond side of the second fibrous web. The third facing layer may beadhesively compatible with the sheath of the bi-component fibres of thesecond fibrous web. The method may further comprise heating the secondfibrous web to a temperature sufficient to soften the sheath material ofat least some of the bi-component fibres. The method may furthercomprise pressing the third facing layer and the second fibrous webtogether under low pressure such that at least part of the third facinglayer contacts the softened sheath material of at least some of thebi-component fibres to form an adhesive bond between the third facinglayer and the second fibrous web.

The bi-component fibres may be blended within the structure of thefibrous web. The bi-component fibres are formed of short lengths choppedfrom extruded bi-component fibres. The core of the bi-component fibresmay have a linear mass density of between about 2 and about 6 Denier perfibre filament. The bi-component fibres may have a sheath to core ratio(in cross-sectional area) of about 25% to 35%, for example about 30%.The bi-component fibres may have a staple length between about 3-4millimetres up to around 70 millimetres for carded fibrous webs. Forexamples described herein, the length of the bi-component fibres isbetween about 32 to about 64 millimetres, with an average or commonlength of about 51 millimetres staple length, being typical of thoseused in fibre carding processes. Short bicomponent fibres may be used insome other nonwoven processes, such as the formation of air laid fibrouswebs.

The facing layer may be adhered only to the sheath material of thebi-component fibres in the fibrous web. In some embodiments, the lowdensity fibrous web is a porous bulk absorber with an air flowresistivity of more than about 1,000 and less than about 60,000 mksRayls/m. The air flow resistivity may alternatively be between about2,500 and about 40,000 mks Rayls/m or between about 3,000 and about20,000 mks Rayls/m. The air flow resistivity may alternatively be about5,600 mks Rayls/m.

The low density fibrous web may have a bulk density of less than about120 kg/m³. Alternatively, the density may be less than about 60 kg/m³.Alternatively, the density may be less than about 30 kg/m³.Alternatively, the density may be less than about 15 kg/m³. The densitymay be as low as about 10 kg/m³, but will generally be higher due topractical considerations, such as mechanical integrity. The density ofthe examples described herein vary between about 14 and about 56 kg/m³.

In some embodiments, the facing layer may comprise a linear low densitycoextruded polyethylene film of about 15 microns thickness.

The fibrous web may be produced by a nonwoven manufacturing processinvolving blending adhesive bi-component fibres and conventional staplefibres and forming a web. The fibrous web may be formed by cross lapped,vertically lapped, air-laid, or other typical nonwoven web-formingprocesses. After web formation, the fibrous web may be bonded by throughair bonding, or may be mechanically consolidated, for example by aneedling process. Subsequent to mechanical consolidation, the fibrousweb may be thermally bonded. The described embodiments are not limitedin relation to fibre orientation.

The adhesive sheath material of the bi-component fibres may be formedfrom low surface energy polymers that are adhesively compatible with theselected facing layer or layers. Polymers for the adhesive sheath of thebi-component fibres may be selected from the group consisting ofpolyethylene, polypropylene, polyamide and co-polyester. The core of thebi-component fibres may be polyester, for example.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are described in further detail below by way of exampleonly, with reference to the accompanying drawings and examples, inwhich:

FIG. 1 is a flowchart of an embodiment of a method of manufacture of asound absorption material;

FIG. 2 is a plot of sound absorption coefficient against frequency forExamples 1 and 2;

FIG. 3 is a plot of sound absorption coefficient against frequency forExamples 3, 4 and 5;

FIG. 4 is a plot of sound absorption coefficient against frequency forExamples 6, 7 and 8;

FIG. 5 is a plot of sound absorption coefficient against frequency forExamples 9 and 10;

FIG. 6 is a schematic diagram of a sound absorption material shown incross-section;

FIG. 7 is a schematic diagram of a process for producing a fibrous webfor a sound absorption material;

FIG. 8 is a schematic diagram of a system for producing a soundabsorption material;

FIG. 9 is a schematic diagram of a system for producing a multi-layeredsound absorption material;

FIG. 10 is a cross-sectional view of the multi-layered sound absorptionmaterial;

FIG. 11 is a flow chart of a method of producing a multi-layered soundabsorption material; and

FIG. 12 is a plot of sound absorption coefficient against frequency forExamples 11, 12 and 13.

DETAILED DESCRIPTION

In dry lamination, a thermoplastic resin is melted to cause adhesionbetween the facing material and the substrate. In some cases, the facingmay comprise a low melting point material that will itself act as a“self-adhesive” facing with the application of heat. Alternatively, anadhesive may be applied in the form of a dry thermoplastic hot meltresin in the form of powder, web, net, spray, or film. The heat to meltthe adhesive resin is applied by direct contact, for example hotcalendar, or indirectly, for example infra-red radiation or hot air. Theadhesive must be selected carefully so as to ensure a good adhesion bothto the facing and substrate. For good adhesion, the surface energy ofthe adhesive must be less than the surface energy of the substrate.

In wet lamination, water and solvent based adhesives are used to provideadhesion between a facing material and a substrate. Again, the adhesivemust be selected carefully so as to ensure a good adhesion to both thefacing and the substrate.

Apart from surface energy, the parameters defining effective adhesion bydry lamination, of a facing to a fibrous web are temperature, pressure,and the period for which the heat is applied. If the contact time isshort, as with a hot roller, then adhesion requires the use ofrelatively high temperatures and higher pressures. This compromises thethickness of the fibrous web unless it has sufficient density to resistthe compressive effects of hot roller lamination.

The addition of a thin membrane facing to a porous bulk absorber canprovide much greater sound absorption than for the porous bulk absorberalone. The thin impermeable film acts as a membrane sound absorber,exhibiting a peak in sound absorption corresponding to the resonantfrequency of the film and the depth of space behind the membrane, whichcorresponds with the thickness of the porous bulk absorber. In addition,the porous bulk absorber couples to the membrane and provides amechanical and acoustic impedance to the overall system, thus providinga broad spectrum of sound absorption around the resonant frequency ofthe membrane.

To achieve effective sound absorption over a broad spectrum, the porousbulk absorber should have a low modulus so that it does not impartstiffness to the membrane. In other words, the porous bulk absorber,which is in this instance a fibrous web acting as a laminatingsubstrate, should be as soft as is feasible, or have a low compliance.In addition, the film membrane should also be soft and flexible. Forexample, a light plastic film is appropriate as the film membrane. In anideal situation the membrane would simply be placed onto the substratewithout any adhesion at all, however this must be rendered into practiceso that the membrane is allowed to float as freely as possible relativeto the porous bulk absorber, while still maintaining adhesion thereto.This requires that the fibrous web, acting as the porous bulk absorber,be particularly soft, and that the film facing layer is adhered with ahigh degree of flexibility so that the film facing layer, acting as amembrane, has a high degree of freedom.

Fibre-based porous bulk sound absorption materials with impermeablesingle or double-sided thin film facings can be used to achieve a verylightweight, highly sound-absorbing composite that provides soundabsorption equivalent to much thicker and heavier unfaced materials.These laminates can be manufactured using cross-laid thermally bondedporous bulk fibrous absorbers. However, fibrous webs having fibres thatare aligned to some extent in the vertical direction (that is in thedirection perpendicular to the machine, and cross, direction of theweb), demonstrate superior mechanical integrity and resistance todelamination due to the orientation of the fibres. Such a constructioncan be found in vertically-laid thermally bonded porous bulk fibrousabsorbers, manufactured for instance by the Struto or V-Lap processes,and is also found to a lesser degree in some airlaid nonwoven fibrouswebs.

Thin membrane-faced sound absorbers can use less raw material, and canbe produced with less energy, and can provide more sound absorption andsignificantly reduced environmental impact compared with heavier, lessefficient porous bulk absorbers. These laminates can be manufacturedusing hot melt adhesive films, applied through a flat bed laminatorunder controlled temperature, pressure and contact time. The expensivehot melt films can be replaced by thin plastic films, such as those usedin diaper manufacture, adhered to the web by a scatter application ofhot melt adhesive powder or similarly effective adhesive applied to thefibrous web.

Because powder scatter application can only be applied to one side of aweb, a hot melt film can be applied to the underside of the web, and apowder scatter application and thin plastic film can be applied to theupper side of the web, so producing a double-faced laminate, ie afibrous web with both a first and second facing layer. This laminate hasthe advantage of providing a product which, when applied in use in avehicle, for example, does not require separate left and right handedcomponents.

Described embodiments relate to the production of sound absorptionmaterials having a self-laminating fibrous web that will adhere to acompatible facing layer, without the need for any adhesive layers, andeliminate the need for the use of any additional adhesives, such asadhesive powders, webs, films, or nets, or any other form of adhesive.The adhesion provided is sufficiently strong, but quite flexible,allowing the membrane to float relatively freely, and optimising theresultant sound absorption.

Some described embodiments involve producing single-side film facedsound absorption material without the need to use either a hot melt filmor any additional adhesives, such as adhesive powders, webs, films, ornets. Some described embodiments involve producing double-side filmfaced sound absorption materials in a single lamination process withoutthe need to use either a hot melt film or any additional adhesives, suchas adhesive powders, webs, films or nets. Further embodiments involvetwo porous bulk absorber layers with a film facing layer therebetweenand film facing layers on each outside face of the double-layered porousbulk absorber material.

Referring now to FIG. 1, a flowchart of a method 100 for manufacturing asound absorption material is described in further detail.

A sound absorption material of the described embodiments can be producedaccording to method 100, which starts at step 110 by forming andmechanically consolidating or thermally bonding a low density (porous)fibrous web with a plurality of bi-component fibres blended within it.Step 110 may comprise a web forming process 700 as described below inrelation to FIG. 7. Each bi-component fibre has a core material and anadhesive sheath, the sheath having a lower melting point than the corematerial. The blending of the bi-component fibres in the fibrous web maybe performed by standard mixing or blending techniques to blend openedstaple fibres with a proportion of opened bi-component fibres.

The temperature differences between the melting points of different coreand sheath materials depend on the specific materials selected. However,the melting point of the sheath material should be sufficiently lowerthan the melting point of the core material in order to allow the corematerial to retain structural integrity while the sheath materialsoftens at a temperature around its melting point temperature. For apolyethylene sheath material, for example, the melting point may bearound 140 to 160° C. Alternatively, temperatures outside this range maystill achieve softening of the polyethylene sheath material, whileallowing structural integrity of the core material to be retained. Inanother example, a polypropylene sheath material may have a meltingtemperature in the order of 180° C. or so. Thus, the temperature atwhich the sheath material softens depends on the melting point of theparticular sheath polymer selected to form the sheath material of thebi-component fibres.

The fibrous web can be formed by nonwoven processes includingcross-lapping, vertical lapping, needle-punching, air laying or anothersuitable method of producing a blended web of nonwoven material,combined with appropriate mechanical consolidation or thermal bonding sothat the web can be handled. The low density fibrous web formed by thisprocess acts as a porous bulk absorber and has an air flow resistivityof more than about 1,000 and less than about 60,000 mks Rayls/m. The airflow resistivity may alternatively be between about 2,500 and about40,000 mks Rayls/m or between about 3,000 and about 20,000 mks Rayls/m.The air flow resistivity may alternatively be about 5,600 mks Rayls/m.The density of the fibrous web may be between about 10 kg/m³ and about120 kg/m³.

At step 120, a film layer is applied as a facing layer to the lowdensity fibrous web and heat is applied at step 130 such that the sheathof the bi-component fibre softens. Steps 120 and 130 may be performedusing a dry lamination system 800 as shown in FIG. 8. For example, for apolyethylene sheath material, the temperature may be between about 140°C. and about 160° C., and possibly about 150° C., for example.

The heat may be applied during (or immediately prior to) the applicationof the facing layer or afterwards. The amount of heating is controlled,and the facing layer is selected, such that under some circumstancesonly the sheath softens. Under other circumstances, where the facinglayer comprises a film layer, the film may also soften to some extentbut does not become molten. The temperature of the heating is selectedso that the structural integrity of the fibrous web and film laminate issubstantially maintained during the heating process. The core materialhas a sufficiently higher melting point than the sheath material toensure that the core material substantially retains its structuralintegrity during the lamination despite the softening sheath.

The film layer is selected to be adhesively compatible with the materialof the sheath so that an adhesive bond can be created between thesheaths of the bi-component fibres and the film. In other words, thesheath and film have relative surface energies such that they are ableto form a strong adhesive bond. Suitable combinations of bi-componentfibre and film include generally include polyethylene terephthalate(PET) as a core polymer, and another lower melting point polymer as anadhesive sheath, for example:

-   -   PET core bi-component fibre having a polyethylene sheath, with a        polyethylene film;    -   PET core bi-component fibre having a polypropylene sheath, with        a polypropylene film;    -   PET core bi-component fibre having a polyamide sheath, with a        polyamide film; and    -   PET core bi-component fibre having a co-polyester sheath, with a        polyester film.

These examples reflect the common forms of bicomponent fibre that arecommercially available. However other combinations of core and sheathmaterial are possible and the above examples should be construed asnon-limiting.

In some embodiments, a combination of bi-component fibres of differenttypes may be used. For example instead of the fibrous web having 30%PE/PET bi-component fibres, 10% CoPET/PET and 20% PE/PET bi-componentfibres may be used. The ratio of bicomponent fibres will generally beselected so that the minimum amount of bicomponent fibre required toachieve suitable adhesion and mechanical integrity is used, so as tominimise cost associated with the more expensive bi-component fibres.

The film layer and fibrous web are brought together under low pressureat step 140, for example using a flat bed laminator 850 as shown in FIG.8, such that at least part of the film layer contacts the softenedsheaths of at least some of the bicomponent fibres to form an adhesivebond without substantial compression or plastic deformation of thefibrous web. The pressure applied to the fibrous web is to aid theadhesion of the film to the fibrous web and not to significantly changethe thickness of the fibrous web. According to the Examples describedherein, compression of the fibrous web and film layer did not result inthe formation of a crust within the fibrous web. Formation of a crustwould result in having increased stiffness and decreased soundabsorption properties.

At step 150, the adhered fibrous web and facing layer are allowed tocool in order to fix the adhesive bond therebetween.

Although the above description of method 100 refers to a single facinglayer being laminated to the fibrous web, facing layers can be appliedto both sides of the fibrous web at step 120 and the double facedfibrous web is heated at step 130 and compressed under relatively lowpressure at step 140, as shown and described below in relation to FIG.8. The double film-faced porous bulk absorber has been found to be evenmore effective at sound absorption than the single film-faced bulkabsorber.

Referring now to FIG. 6, there is shown a cross-sectional schematicrepresentation of a sound absorption material 200 according to someembodiments. The sound absorption material 200 comprises a facing layer210 and a fibrous web 220 having a number of bi-component fibres 230blended therein. The facing layer 210 is adhered to the fibrous web 220by an adhesive bond formed between facing layer 210 and a sheath 211 ofsome of the bi-component fibres 230 located within fibrous web 220adjacent the face of fibrous web 220 to which facing layer 210 isapplied.

Bi-component fibres 230 each have the sheath 211 formed around a corematerial 212. The sheath 211 has a melting point sufficiently lower thanthe melting point of core material 212 so that a temperature can beselected at which to melt or soften the sheath material 211 for adhesionto facing layer 210, without substantially affecting the structuralintegrity of the core material 212.

The fibrous web 220, facing layer 210 and bi-component fibres 230 ofFIG. 6 have the properties described herein and may be used to form thesound absorption material as described herein and/or according to theExamples.

Although the sound absorption material 200 is shown in FIG. 6 as havingonly a single facing layer 210 applied to one side of the fibrous web220, another facing layer, either being of the same material as facinglayer 210 or another thin facing layer material as described herein, maybe applied to the other side of the fibrous web 220, being adhered tothe sheath material 211 of the bi-component fibres 230 in a similarmanner. Either or both of the facing layers 210 may have materialcharacteristics suitable for enabling ultrasonic welding of the soundabsorption material 200 to a surface, such as a plastic moulding for thedoor trim of a vehicle. For such embodiments, the facing layer must becompatible with the material of the plastic molding substrate, which mayin some embodiments comprise talc-filled polypropylene.

In some embodiments, the sound absorption material 200 may be made tohave a density of about 350 gsm and be about 25 mm thick with a doublesided film facing layer suitable for ultrasonic welding to vehicle doortrims. Provision of the sound absorption material 200 in such a mannercan eliminate the need for anti-rattle pads to be applied to thevehicle, thereby reducing vehicle manufacturing costs and reducing thenumber of components needed to be installed in the vehicle. It has beenfound that a low density is desirable for achievement of effective soundabsorption. This means that thick materials can be achieved with arelatively low amount of fibre, without sacrificing sound absorption forthe purposes of achieving such anti-rattle properties.

Embodiments of sound absorption materials described herein are generallycharacterised as being self-laminating as there is no need for adhesivesto be used to adhere the facing layers to the fibrous web (except wherenoted below in relation to sound absorption materials having a doublelayered fibrous web). Additionally, because the fibrous web used in thesound absorption material 200 or 1000 (FIG. 10) is low density, it ispossible to manually handle large rolls of such materials withoutspecial lifting devices.

Fibrous web 220 may be a carded, vertically-lapped, thermally bondedweb. Fibrous web 755 (FIG. 7) is an example of fibrous web 220.Alternative fibrous webs may include carded cross-lapped and needlepunched webs, air-laid webs, melt-blown webs and combinations of these.Alternative web bonding types may include resin bonding and mechanicalbonding, such as needle punching or hydro-entangling.

Facing layer 210 may comprise a thin flexible cast coextruded film, suchas is produced by Stellar Films Group of Melbourne, Australia. The filmmay comprise a three-ply film consisting of linear low densitypolyethylene (LLDPE) with an adhesive tie-layer, for example. The filmmay have a small percentage of metallocene LLDPE in it to improvesoftness and mechanical properties, such as tear strength and elongationand to reduce noise. Other films, such as polypropylene and polyesterfilms, may be used in alternative embodiments. However, metallocenepolyolefins can be advantageous as they can provide improved mechanicalproperties, such as toughness, and can be used at lower thicknesses.

Steps 130 and 140 described above in relation to method 100 may beperformed simultaneously, for example by having the fibrous web andsingle or double thin facing layers feed into a flat-bed laminator 850(FIG. 8) for dry lamination between heated Teflon belts. Such alaminator should allow for the application of gentle pressure over aperiod of time, so that the integrity of the fibrous web is not affectedand the thickness of the fibrous web is not overly reduced during thelamination process. However, not all flat bed laminators are suitable.The top belt needs to be prevented from drooping, as this will reducethe thickness of the sound absorption material undesirably. As thefibrous web is commonly quite soft and cannot support the belt weight,particularly as the web is heated and the adhesive fibres soften, it isimportant that the top belt of the laminator does not droop.

The self-laminating fibrous web (by virtue of the film compatiblebi-component fibres blended in the web) obviates the need for othercommon features of dry lamination systems, such as hot melt adhesives,powders, film, nets and webs. In effect, the sound absorption materialsusing a fibrous web with bi-component fibres blended therein can be seenas incorporating an adhesive web in the fibre blend.

The flat bed laminator 850 or 950 (FIG. 9) is configured to apply aspecific temperature and pressure to the fibrous web or webs and filmlayer or layers for a predetermined period of time (controlled byadjusting the speed of progress of the material through the laminator).

Referring now to FIG. 7, a process 700 for forming a fibrous web 755 isdescribed in further detail. The fibrous web 755 comprises a blend ofstandard polyester fibres 705 and bi-component fibres 707 that areopened and mixed in a bale opener and mixing system 720. The blendedfibres are then carded using a carding system 730 before undergoing webformation 740. The output of the web formation 740 may be a verticallylapped but unbonded web 745, which is then passed through a thermalbonding system 750 to provide thermal bonding among the thermoplasticfibres of the vertically lapped web 745. The thermally bonded fibrousweb 755 may then be used as the fibrous web 220 as part of the soundabsorption material 200. Alternatively, the fibrous web 755 may be usedin the formation of sound absorption materials, as shown and describedin relation to FIGS. 8 to 11.

Referring now to FIG. 8, a system 800 for forming sound absorptionmaterial is described in further detail. System 800 may receive a bondedfibrous web 755, either directly from the process 700 or unrolled from aroll of such fibrous web material. System 800 comprises a film unwinder(not shown) positioned to unwind film 815 from a roll 812 of such filmto form the facing layer on one side of the fibrous web 755. The fibrousweb 755 and film 815 may be conveyed by a conveyor (not shown) to flatbed laminator 850.

If system 800 is to be used to produce a double film faced soundabsorption material 940, a further film 840 is unwound from a roll 845and applied to the face of fibrous web 755 that is opposite to the sideon which film 815 is applied. Film 840 may be applied to the fibrous web755 simultaneously with film 815 and film facing layers 815 and 840 arethen fed into flat bed laminator 850 together.

Flat bed laminator 850 may have separated top and bottom belts 852, eachpassing over a series of rollers to convey the fibrous web 755 and filmfacing layers 815, 840 through the laminator 850. Rollers 856 arepositioned at the entry of the laminator 850 to lightly press thematerials together as they enter the laminator 850. Laminator 850 has aheating section 862 and a cooling section 864 for successively heatingthen cooling the material layers (755, 815 and 840) as they passthrough. A nip roller 868 is located on both top and bottom belts 852 inbetween the heating and cooling sections 862, 864 to slightly compressthe heated material layers (755, 815 and 840) together before they arecooled to fix the adhesion of the bi-component fibres of fibrous web 755with the respective film layers 815, 840. The heating section 862 oflaminator 850 is configured to heat the material to between about 140degrees C. and about 160 degrees C.

Referring now to FIGS. 9 to 11, a system 900 for producing a soundabsorption material 1000 according to method 1100 is described infurther detail. System 900 is similar to system 800, except that,instead of film layer 840 being applied to one side of a fibrous web755A, a double-faced sound absorber 940, such as may be produced bysystem 800 according to method 100 at step 1110, is applied as a secondlayer on top of the first fibrous web layer 755A. Additionally, as aflat bed laminator 950 will generally be inadequate to providesufficient heat to achieve adhesion of the bi-component fibres in thefibrous web layer 755A with the film layer 815 of the fibrous web layer755B, an activated adhesive, such as an adhesive powder, is applied tothe exposed side of fibrous web layer 755A prior to application of thedouble-faced sound absorber and subsequently passing the double-layeredfibrous web material through flat bed laminator 950.

System 900 comprises a film roll 912 positioned in an unwinder (notshown) to apply (at step 1130) a film 915 as an external facing layer onone side of fibrous web 755A formed by process 700 at step 1120. Fibrousweb 755A and film layer 915 are passed through an adhesive applicator920, such as a powder scattering unit, which scatters or otherwiseapplies (at step 1140) an adhesive substance 922, such as an adhesivepowder, onto the side of the fibrous web 755A opposite to the side towhich film 915 is applied. Adhesive substance 922 will generally beapplied to an upwardly facing side of fibrous web 755A. Adhesivesubstance 922 is then activated at step 1150 as it passes through anactivation mechanism 930, such as an infra-red heater that transmitsinfra-red radiation 932 to heat-activate the adhesive substance 922.Instead of an adhesive powder, a suitable adhesive film may be appliedto fibrous web 755A using the adhesive applicator for subsequentactivation and adhesion.

A roller 945 is used to apply the fibrous web layer 755B onto theexposed side of the first fibrous web layer 755A that has the activatedadhesive thereon. The adhesive substance 922 is selected to beadhesively compatible with the film layer 815 and fibrous web 755A. Theadhesive substance may comprise, for example, LDPE or polyamide powder.

In some embodiments, instead of applying adhesive to the top surface ofthe fibrous web 755A, heat may be applied to the top surface to softenthe sheath material of the bi-component fibres 230, which can then forma light adhesive bond when film facing layer 815 is lightly pressedtogether with fibrous web 755A. Thus, such embodiments may comprise noadditional adhesive beyond the softened bi-component fibres in thefibrous web 755A and may substitute the described heating step for steps1140 and 1150.

Flat bed laminator 950 may have separated top and bottom belts 952, eachpassing over a series of rollers to convey the fibrous webs 755A, 755Band film facing layers 815, 840 and 915 through the laminator 950.Rollers 956 are positioned at the entry of the laminator 950 to lightlypress the materials (755A, 755B, 815, 840 and 915) together (at step1160) as they enter the laminator 950. Laminator 950 has a heatingsection 962 and a cooling section 964 for successively heating thencooling the material layers (755A, 755B, 815, 840 and 915) as they passthrough. A nip roller 968 is located on both top and bottom belts 952 inbetween the heating and cooling sections 962, 964 to slightly compressthe heated material layers (755A, 755B, 815, 840 and 915) together atstep 1170 before they are cooled at step 1180 to fix the adhesion of thebi-component fibres of fibrous web 755A with the film layer 915. Thepressing at step 1160 and light compression at step 1170 also serves toaid adhesion of the film layer 815 with fibrous web 755A by means of theadhesive substance 922. The heating section 962 of laminator 950 isconfigured to heat the material to between about 140 degrees C. andabout 160 degrees C.

Conveyors (not shown) may be used to carry the fibrous web layer 755Aand film layer 915 into flat bed laminator 950, along with the preformedsound absorption material 940 comprising the second layer of fibrous web755B with film layers 815 and 840, for heating and slight compression(at steps 1160 and 1170). The flat bed laminator 950 applies arelatively low pressure to these materials to achieve adhesion betweenthe fibrous web 755A and film layer 815 via adhesive substance 922 andbetween fibrous web 755A and film 915 via adhesion of the sheathmaterial of the bi-component fibres blended into fibrous web 755A withfilm layer 915.

The output of flat bed laminator 950 is shown in a larger scale in FIG.10 as double layered sound absorption material 1000. FIG. 10 is notto-scale and is provided for illustrative purposes, not as a physicallyand dimensionally accurate representation of the described embodiments.Some embodiments employ vertical lapping as part of the web formationprocess, so the vertically oriented wave forms in fibrous webs 755A and755B illustrated in FIG. 10 are intended only to indicate this verticallapping as one kind of possible web form, rather than to illustrate aspecific fibre shape, structure or dimension.

Sound absorption material 1000 has two fibrous web layers 755A and 755B,with a thin facing layer 815 therebetween and thin facing layers 840 and915 on the outer faces of the resultant composite sound absorptionmaterial 1000. Depending on the bonding process, an adhesive layer maybe formed by adhesive powder 922 or another adhesive substance. Soundabsorption material 1000 may have a thickness X of about 10 mm to about80 mm, for example. Fibrous web layers 755A and 755B may haveapproximately the same thickness or may have different thicknesses.Additionally, thin facing layers 815, 840 and 915 may compriseessentially the same material or may be formed of different materials,provided that those materials are adhesively compatible with the sheathmaterial of the bi-component fibres blended into the fibrous web layers755A and 755B.

The material characteristics of the fibrous webs 755A and 755B, the thinfacing layers 815, 840 and 915 are as described as above. While FIG. 10shows the fibrous web layers 755A and 755B as being vertically lapped,other suitable fibrous web structures may be employed.

The embodiments described herein in relation to FIGS. 1 and 7 to 11 arepresented by way of example only. Where appropriate, alternativesystems, methods and materials can be substituted for those described,provided that similar features and functions are obtained as describedherein.

EXAMPLES

Several samples of fibrous web were prepared, each being a verticallylapped thermally bonded non-woven web with a nominal web weight ofbetween 200 gsm and 400 gsm and approximately 3-5 mm thicker than therequired finished product. Some of the fibrous webs (Blend 1) have astaple polyester fibre blended with a bi-component adhesive fibrecomprising a co-polyester sheath and polyester core. The remainingfibrous webs (Blend 2) have a polyester fibre blended with an adhesivefibre consisting of a polyethylene sheath with a polyester core in lieuof the polyester bi-component fibre. Details of each Blend appear inTable 1.

TABLE 1 Fibre Blend 1 2 2Denier bicomponent (CoPET/PET) 30% 2Denierbicomponent polyolefin/polyester fibre 30% 3Denier regenerated PET RSF(regular staple fibre) 40% 40% 12Denier SHCSF (spiral hollow conjugate30% 30% staple fibre) PET Nominal web density, g/m². 200 350 Laminatingtemperature, C. 150 150 Laminator belt speed, m/minute 5 5

Plastic films were then laminated to the webs using a Schaetti flat-bedlaminator. Similar laminators are provided by Meyer, Reliant and Glenro.In each case, the laminator belts were heated and the belt height wasset to the required finished thickness. The samples were run through thelaminator at a speed of about 5 m/minute.

Comparative examples were produced using conventional adhesive-typefilms that are re-activated by the heat of the dry-lamination process. A25 micron polyurethane thermoplastic film, manufactured by Ding Zing ofTaiwan, was laminated to webs produced from Blend 1, referred to asExample 1 during testing.

A 20 micron unslit co-extruded hot melt film, type Xiro V4712,manufactured by Collano of Switzerland, was laminated to webs producedfrom Blend 1, referred to as Examples 4 and 7 during testing. A furtherlayer of Xiro V4712 was also laminated to the other side to form adouble sided product, referred to as Example 9 during testing.

A 15 micron linear low density polyethylene (LLDPE) cast coextruded3-layer film was provided as a surface facing to be laminated to websproduced from Blends 1 and 2. This film, although thermoplastic, wouldnot adhere to Blend 1 during the lamination process, without theapplication of a low density polyethylene (LDPE) adhesive powder of 500micron particle size, referred to as Examples 3 and 6 during testing.

The same LLDPE film was laminated to Blend 2 during the laminationprocess and adhered successfully without the need for adhesive powder,referred to as Examples 2, 5 and 8 during testing. The PE sheath on thePE/PET bi-component binder has a lower melting point than the LLDPE filmand suitable melt-flow and adhesive properties that render it as anexcellent adhesive for LLDPE film, thus providing an adhesive that isincorporated into the web itself, making it unnecessary to use athermoplastic adhesive film, or an additional adhesive, such as anadhesive powder. A further LLDPE film layer was laminated to the otherside of the laminate to form a double sided product, referred to asExample 10 during testing.

The samples were then tested for sound absorption in an impedance tubeusing the two microphone technique, in accordance with ASTM 1050E.

The sound absorption of the samples produced from Blend 2, laminatedwith the LLDPE film exhibited measurably higher sound absorption thanall of the other samples.

From FIG. 2, increased sound absorption can be seen in theself-laminating web, (Example 2) compared to a thermoplasticpolyurethane hot melt film (Example 1), particularly at frequenciesabove 400 Hz.

From FIG. 3, increased sound absorption can be seen in the soundabsorption material formed using the self-laminating LLDPE film (Example5), when compared to powder laminated (Example 3) and co-extruded hotmelt films (Example 4), particularly at frequencies above 400 Hz.

From FIG. 4, increased sound absorption can be seen in theself-laminating web (Example 8), compared to powder laminated (Example6) and hot melt films (Example 7). For these examples, the soundabsorption is greater than for previous examples, due to the higher webdensity compared to those examples. In particular, Example 6 has a webdensity of 400 gsm whilst Example 8 has a web density of only 350 gsm.Both use the same film laminated with either powder or with theself-laminating web. Despite the higher web mass in Example 6, the soundabsorption is still significantly less than for Example 8, indicatingthat the improvement in sound absorption through the use of theself-laminating web is significantly greater than achieved by anincrease in web weight.

From FIG. 5, laminating a film to both sides of the web further improvesthe sound absorption of a film-laminated web, but more particularly soin the case of the self-laminating web. Example 10 demonstrates a largeincrease in sound absorption compared to Example 9. Again this isdespite the higher mass of the web in Example 9, which would normallyimply greater sound absorption.

A hybrid blend of Blend 1 (e.g. 15%) and Blend 2 (e.g. 15%) may be usedto similar sound absorption effect.

In Examples 11, 12 and 13, two layers of film faced sound absorptionmaterials were combined, one on top of the other, as shown and describedin relation to FIGS. 9, 10 and 11. The sound absorption was measuredaccording to ISO 1050, but only using a small 27 mm tube. The materialproperties of the double-layered sound absorption material are providedin Table 2 below.

TABLE 2 Example 11 Example 12 Example 13 Film Description Linear LowDensity Linear Low Density Linear Low Density Polyethylene clearPolyethylene clear Polyethylene clear embossed film 15 μm embossed film15 μm embossed film 15 μm (app 14.5 gsm) (app 14.5 gsm) (app 14.5 gsm)Adhesive mechanism Adhesive fibres Adhesive fibres Adhesive fibres &LDPE adhesive powder Nominal web density, g/^(m2), 350  200  200  layer1 Nominal web density, g/^(m2), 350  350  350  layer 2 Nominalthickness, mm, layer 1 20 17 16 Nominal thickness, mm, layer 2 20 23 23Nominal total thickness, mm 40 40 39

As FIG. 12 illustrates, the results indicate a substantial boost inlower frequency sound absorption, without compromising the highfrequency sound absorption characteristics. It suggests an increase insound absorption achieved by creating a multi-layer composite of theself-laminating sound absorption material 200, when constructed asdescribed herein and according to Examples 11, 12 and 13.

Acoustic weight efficiency is defined as the noise reduction coefficient(NRC) divided by the mass of the material. The NRC is the average of thesound absorption coefficients measured at each of the frequencies of250, 500, 1000, and 2000 Hz. The acoustic weight efficiency of somedescribed embodiments and/or samples is appreciably higher thancommercial products, such as acoustic felts produced by The Smith Familyof Sydney, Australia. The inventors consider that the describedembodiments provide sound absorption materials that provide higher soundabsorption performance with lighter weight. This feature can beimportant in automotive applications as a weight reduction can improvethe fuel economy of vehicles using sound absorption materials.

The reference in this specification to any prior publication (orinformation derived from it), or to any matter which is known, is not,and should not be taken as an acknowledgment or admission or any form ofsuggestion that that prior publication (or information derived from it)or known matter forms part of the common general knowledge in the fieldof endeavour to which this specification relates.

Throughout this specification and the claims which follow, unless thecontext requires otherwise, the word “comprise”, and variations such as“comprises” and “comprising”, will be understood to imply the inclusionof a stated integer or step or group of integers or steps but not theexclusion of any other integer or step or group of integers or steps.

Embodiments have been described herein with reference to the figures andexamples. However, some modifications to the described embodimentsand/or examples may be made without departing from the spirit and scopeof the described embodiments, as described in the appended claims.

1. A method of manufacturing a sound absorption material, the methodcomprising: forming a low density fibrous web to act as a porous bulkabsorber, the fibrous web containing a proportion of bi-componentfibres, each bi-component fibre having a core material and a sheathmaterial around the core material, the sheath material having a lowermelting point than the core material; applying a thin facing layer tothe low density fibrous web, wherein the facing layer is adhesivelycompatible with the sheath material; heating the fibrous web to atemperature sufficient to soften the sheath material of at least some ofthe bi-component fibres; pressing the facing layer and fibrous webtogether under low pressure such that at least part of the facing layercontacts the softened sheath material of at least some of thebicomponent fibres to form an adhesive bond between the facing layer andthe fibrous web. 2.-5. (canceled)
 6. The method of claim 1, wherein athickness of the fibrous web after the pressing is reduced by about 5%to 80% of the thickness of the fibrous web before the pressing. 7.-12.(canceled)
 13. The method of claim 1, wherein the facing layer is afirst facing layer applied to a first face of the fibrous web and themethod further comprises applying a second facing layer to a second faceof the fibrous web, the second facing layer being adhesively compatiblewith the sheath.
 14. The method of claim 13, further comprising pressingthe second facing layer and the fibrous web together under low pressuresuch that at least part of the second facing layer contacts the softenedsheath of at least some of the bi-component fibres to form an adhesivebond between the second facing layer and the fibrous web. 15.-16.(canceled)
 17. The method of claim 13, wherein the fibrous web is afirst fibrous web and the method further comprises pressing a second lowdensity fibrous web together with the second facing layer under lowpressure to lightly bond a first side of the second fibrous web to thesecond facing layer, wherein the second fibrous web comprises aproportion of bi-component fibres each having a core material and asheath material around the core material, the sheath material having alower melting point than the core material.
 18. The method of claim 17,further comprising, prior to pressing the second fibrous web togetherwith the second facing layer, heating the first side of the secondfibrous web to soften the sheath material of the bi-component fibres inthe second fibrous web so that an adhesive bond can be formed betweenthe second fibrous web and the second facing layer when pressed togetherunder low pressure.
 19. The method of claim 17, further comprising,prior to pressing the second fibrous web together with the second facinglayer, applying an adhesive substance to the first side of the secondfibrous web, the adhesive substance being adhesively compatible with thesecond facing layer. 20.-22. (canceled)
 23. The method of claim 17,further comprising: applying a third facing layer to a second side ofthe second fibrous web, the third facing layer being adhesivelycompatible with the sheath material of the bi-component fibres of thesecond fibrous web; heating the second fibrous web to a temperaturesufficient to soften the sheath material of at least some of thebi-component fibres; and pressing the third facing layer and the secondfibrous web together under low pressure such that at least part of thethird facing layer contacts the softened sheath material of at leastsome of the bi-component fibres to form an adhesive bond between thethird facing layer and the second fibrous web. 24.-26. (canceled)
 27. Asound absorption material formed by the method of claim
 1. 28. A soundabsorption material comprising: a low density fibrous web to act as aporous bulk absorber, the fibrous web containing a proportion ofbi-component fibres, each bi-component fibre having a core material anda sheath material around the core material, the sheath material having alower melting point than the core material; and a thin facing layeradhered to the fibrous web by an adhesive bond formed between the sheathmaterial of at least some of the bi-component fibres and the facinglayer.
 29. The material of claim 28, wherein the thin facing layercomprises material selected from the group consisting of polymer films,foils and fabrics.
 30. The material of claim 28, wherein the thin facinglayer comprises material selected from the group consisting ofpolyethylene, polyester, polyamide and polypropylene.
 31. (canceled) 32.The material of claim 28, wherein the low density fibrous web has adensity of more than about 10 kg/m³ and less than about 120 kg/m³.33.-34. (canceled)
 35. The material of claim 28, wherein the sheathmaterial of the bi-component fibres is selected from the groupconsisting of polyethylene, polyamide, polypropylene and co-polyester.36. The material of claim 28, wherein the thin facing layer comprises afilm layer having a thickness of between 5 and 100 microns. 37.-46.(canceled)
 47. The method of claim 18, further comprising: applying athird facing layer to a second side of the second fibrous web, the thirdfacing layer being adhesively compatible with the sheath material of thebi-component fibres of the second fibrous web; heating the secondfibrous web to a temperature sufficient to soften the sheath material ofat least some of the bi-component fibres; and pressing the third facinglayer and the second fibrous web together under low pressure such thatat least part of the third facing layer contacts the softened sheathmaterial of at least some of the bi-component fibres to form an adhesivebond between the third facing layer and the second fibrous web.
 48. Themethod of claim 19, further comprising: applying a third facing layer toa second side of the second fibrous web, the third facing layer beingadhesively compatible with the sheath material of the bi-componentfibres of the second fibrous web; heating the second fibrous web to atemperature sufficient to soften the sheath material of at least some ofthe bi-component fibres; and pressing the third facing layer and thesecond fibrous web together under low pressure such that at least partof the third facing layer contacts the softened sheath material of atleast some of the bi-component fibres to form an adhesive bond betweenthe third facing layer and the second fibrous web.